The United States of America has certain rights and licenses in this invention.
1. Field of the Invention
The present invention is related to a dual-torch gas metal arc pulse-welding apparatus for use in metal overlay applications. In particular, the present invention relates to an apparatus and process for the application of welded metal overlay deposits to cylindrical substrates for use in wear, chemical, and temperature resistance. More specifically, this invention relates to the application of welded overlay rotating bands to steel and other alloy artillery projectiles.
2. Description of Related Art
A conventional machine is known which employs a single torch gas metal arc-welding torch for overlay applications. Specifically, such a machine has been employed for the application of a gilding metal rotating band to artillery projectiles on the outside diameter of cylindrical metal parts. The conventional machine uses a single gas metal arc-welding torch powered by a standard gas metal arc welding power source. Welding is performed in the direct current electrode positive mode of welding, where the electrode is a continuously-fed electrically-charged wire as in conventional gas metal arc welding Aprocesses. The torch is mounted on an oscillating head, where the oscillating parameters include oscillation frequency and width, and can be controlled as a function of time and/or angular position. In addition to the gas metal arc welding torch, a non-electrically charged auxiliary wire is positioned on the oscillating head such that it maintains a strict alignment with the electrically-charged electrode and maintains a certain variable geometric relationship as shown in FIG. 1. Alignment of the electrode and auxiliary wires is critical and is key to the process. Rotary cam-type wire straighteners are used on both the electrode and auxiliary wire feed systems in order to maintain wire alignment. The welding torch and auxiliary wire are so mounted on the oscillating head that the head may be moved in an x, y or z direction. The welding torch and the auxiliary wire are mounted so that the torch angle may vary from 0 degrees (perpendicular) to 20 degrees, and that the angle between the welding torch and the auxiliary wire is also variable.
In the known process, a continuous overlay deposit is performed around the entire circumference of the substrate part in a single welding sequence. A substrate, such as a metal cylinder, rotates beneath the oscillating torch at a programmable rotation speed, and an overlay deposit of a variable width is applied through the manipulation of parameters, which may include rotational speed of the substrate part, oscillation frequency, electrode wire feed speed, auxiliary wire feed speed, torch height (z), torch location (x), torch off-center position (y), torch angle, and the angle of the auxiliary wire to the torch. A cooling water nozzle is used on the interior of the metal cylinder that follows the torch, and covers the inside surface of the cylinder with a water spray over the width of the torch oscillation. In the known process, electrode wire diameters of 0.035xe2x80x3 through xe2x85x9xe2x80x3 and auxiliary wire diameters of 0.035xe2x80x3 to {fraction (3/32)}xe2x80x3 have been used. Typically, electrode and auxiliary wire diameters are matching, but this is not always necessary, or even desired. Overlay deposits of brass (gilding metal), silicon bronze, copper, nickel, iron, monel, titanium, and stainless steel have been made in this manner.
In most instances, the composition of the electrode and the auxiliary wire are the same, but this may not always be the case. In the case of gilding deposits where the metal deposit is a brass alloy, for example, the electrode is typically copper and the auxiliary wire is a brass alloy, because the zinc contained in the brass alloy cannot be transferred through the welding arc. In monel, a copper electrode may be used in conjunction with a nickel auxiliary wire. This conventional process is capable of achieving low dilution rates and minimal weld penetration on substrates that are both ferrous and non-ferrous alloys. Dilution rates less than 2% have been achieved in the welding of copper alloys, and penetration of less than 0.030xe2x80x3 has been achieved in the welding of nickel alloys. Welding has been performed on a variety of different materials, to include alloy steels, plain carbon steels, high carbon steels, ductile iron, maraging steels, and titanium. Cylinder sizes have typically ranged from 0.5 inches to 6 inches in diameter, and wall thickness have ranged from {fraction (3/16)}xe2x80x3 to xc2xexe2x80x3. The conventional process, however, has shown unacceptable penetration (greater than 0.030xe2x80x3) in wall thickness less than {fraction (3/16)}xe2x80x3.
It is an object of the present invention to provide a dual torch gas metal arc pulse welding apparatus that is capable of applying a metal overlay to cylindrical metal bases with narrower side wall, without unacceptable penetration.
It is a further object of the present invention to provide a dual torch gas metal arc pulse welding apparatus that is capable of the more efficient deposition of a metal overlay to cylindrical metal bases.
It is a still further object of the present invention to provide a process in which a metal overlay may be applied to cylindrical metal bases with narrow sidewalls, without unacceptable penetration.
The other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of the preferred embodiment thereof.
According to one embodiment of the present invention, there is disclosed an apparatus for the overlay of metal on a revolving cylindrical metal base by welding, with minimal penetration, said apparatus comprising:
a first gas metal arc pulse welding apparatus comprising a primary wire direct current electrode capable of positive pulse welding, and an electrically-neutral auxiliary wire,
a second gas metal arc pulse welding apparatus comprising a primary direct current electrode capable of positive pulse welding, and an electrically-neutral auxiliary wire, and,
a cylindrical metal base, which is negatively-charged and rotated in relation to, said first and second gas metal arc pulse welding apparatuses.
According to another embodiment of the present invention, there is disclosed a process for the application of a metal band to a cylindrical metal base, with a dual gas metal arc pulse welding apparatus, which process comprises the steps of:
a. weld arc initiation;
b. weld ramp;
c. weld;
d. initial weld stop;
e. weld overlap; and,
f. arc termination.